Linux设备模型分析之kobject
一、kobject应用举例
Linux设备模型最基本的组成元素是kobject,我们先来看一个kobject的应用例子,该程序在Ubuntu 10.10, 2.6.32-38-generic-pae内核上调试通过。
- #include <linux/device.h>
- #include <linux/module.h>
- #include <linux/kernel.h>
- #include <linux/init.h>
- #include <linux/string.h>
- #include <linux/sysfs.h>
- #include <linux/stat.h>
- MODULE_AUTHOR("haoyu");
- MODULE_LICENSE("Dual BSD/GPL");
- structmy_kobject
- {
- intvalue;
- structkobject kobj;
- };
- structmy_kobject my_kobj;
- voidkobject_release(structkobject *kobject);
- ssize_t kobject_attr_show(structkobject *kobject,structattribute *attr,char*buf);
- ssize_t kobject_attr_store(structkobject *kobject,structattribute *attr,constchar*buf,size_tcount);
- structattribute kobject_attr1 = {
- .name = "name",
- .mode = S_IRWXUGO,
- };
- structattribute kobject_attr2 = {
- .name = "value",
- .mode = S_IRWXUGO,
- };
- staticstructattribute *kobject_def_attrs[] = {
- &kobject_attr1,
- &kobject_attr2,
- NULL,
- };
- structsysfs_ops kobject_sysfs_ops =
- {
- .show = kobject_attr_show,
- .store = kobject_attr_store,
- };
- structkobj_type ktype =
- {
- .release = kobject_release,
- .sysfs_ops = &kobject_sysfs_ops,
- .default_attrs = kobject_def_attrs,
- };
- voidkobject_release(structkobject *kobject)
- {
- printk("kobject release.\n");
- }
- ssize_t kobject_attr_show(structkobject *kobject,structattribute *attr,char*buf)
- {
- intcount = 0;
- structmy_kobject *my_kobj = container_of(kobject,structmy_kobject, kobj);
- printk("kobject attribute show.\n");
- if(strcmp(attr->name,"name") == 0)
- count = sprintf(buf, "%s\n", kobject->name);
- elseif(strcmp(attr->name,"value") == 0)
- count = sprintf(buf, "%d\n", my_kobj->value);
- else
- printk("no this attribute.\n");
- returncount;
- }
- ssize_t kobject_attr_store(structkobject *kobject,structattribute *attr,constchar*buf,size_tcount)
- {
- intval;
- structmy_kobject *my_kobj = container_of(kobject,structmy_kobject, kobj);
- printk("kobject attribute store.\n");
- if(strcmp(attr->name,"name") == 0)
- printk("Can not change name.\n");
- elseif(strcmp(attr->name,"value") == 0)
- {
- val = buf[0] - '0';
- if(val == 0 || val == 1)
- my_kobj->value = val;
- else
- printk("value is '0' or '1'\n");
- }
- else
- printk("no this attribute.\n");
- returncount;
- }
- staticintkobject_test_init(void)
- {
- printk("kboject test init.\n");
- kobject_init_and_add(&my_kobj.kobj,&ktype,NULL,"kobject_test");
- return0;
- }
- staticvoidkobject_test_exit(void)
- {
- printk("kobject test exit.\n");
- kobject_del(&my_kobj.kobj);
- }
- module_init(kobject_test_init);
- module_exit(kobject_test_exit);
该模块执行过程如下图所示:
二、相关数据结构:
kobject是Linux设备模型中最基本的数据结构,代表设备模式的一个基本对象。
kobj_type是kobject的类型,包括kobject的属性以及属性的操作接口,不同的kobject可以具有相同的kobj_type。
kset是几个kobject的集合,这些kobject可以具有相同的kobj_type,也可以具有不同的kobj_type。
三、kobject注册和注销过程分析
kobject的注册是通过调用kobject_init_and_add函数,该函数定义如下:
先来看kobject_init,该函数定义如下:
kobject_init_internal函数定义如下:
至此,kobject_init函数就分析完了,我们返回到kobject_init_and_add函数,下面该分析kobject_add_varg函数了:
然后,调用create_dir(kobj)在/sys目录下建立kobject相关目录结构。
kobj_kset_join函数定义如下:
sysfs_create_dir函数定义如下:
下面来看populate_dir函数,其定义如下:
至此,kobject的注册过程我们就分析完了。
kobject的注销过程是调用kobject_del函数,该函数定义如下:
- /**
- * kobject_del - unlink kobject from hierarchy.
- * @kobj: object.
- */
- voidkobject_del(structkobject *kobj)
- {
- if(!kobj)
- return;
- sysfs_remove_dir(kobj);
- kobj->state_in_sysfs = 0;
- kobj_kset_leave(kobj);
- kobject_put(kobj->parent);
- kobj->parent = NULL;
- }
这里需要注意的是,只要把目录删除,目录下的属性文件自动就删除了。
- /*
- * populate_dir - populate directory with attributes.
- * @kobj: object we're working on.
- *
- * Most subsystems have a set of default attributes that are associated
- * with an object that registers with them. This is a helper called during
- * object registration that loops through the default attributes of the
- * subsystem and creates attributes files for them in sysfs.
- */
- staticintpopulate_dir(structkobject *kobj)
- {
- structkobj_type *t = get_ktype(kobj);
- structattribute *attr;
- interror = 0;
- inti;
- if(t && t->default_attrs) {
- for(i = 0; (attr = t->default_attrs[i]) != NULL; i++) {
- error = sysfs_create_file(kobj, attr);
- if(error)
- break;
- }
- }
- returnerror;
- }
该函数循环遍历kobject的所有属性,并调用sysfs_create_file函数在/sys系统对应目录下建立属性文件。
- /**
- * sysfs_create_dir - create a directory for an object.
- * @kobj: object we're creating directory for.
- */
- intsysfs_create_dir(structkobject * kobj)
- {
- enumkobj_ns_type type;
- structsysfs_dirent *parent_sd, *sd;
- constvoid*ns = NULL;
- interror = 0;
- BUG_ON(!kobj);
- if(kobj->parent)
- parent_sd = kobj->parent->sd;
- else
- parent_sd = &sysfs_root;
- if(sysfs_ns_type(parent_sd))
- ns = kobj->ktype->namespace(kobj);
- type = sysfs_read_ns_type(kobj);
- error = create_dir(kobj, parent_sd, type, ns, kobject_name(kobj), &sd);
- if(!error)
- kobj->sd = sd;
- returnerror;
- }
这里主要是通过调用create_dir函数建立kobject对应的目录。这个函数我们就不继续向下跟踪了。
- staticintcreate_dir(structkobject *kobj)
- {
- interror = 0;
- if(kobject_name(kobj)) {
- error = sysfs_create_dir(kobj);
- if(!error) {
- error = populate_dir(kobj);
- if(error)
- sysfs_remove_dir(kobj);
- }
- }
- returnerror;
- }
首先调用sysfs_create_dir在/sys下建立目录,然后再调用populate_dir在新建目录下生成属性文件。
- /* add the kobject to its kset's list */
- staticvoidkobj_kset_join(structkobject *kobj)
- {
- if(!kobj->kset)
- return;
- kset_get(kobj->kset);
- spin_lock(&kobj->kset->list_lock);
- list_add_tail(&kobj->entry, &kobj->kset->list);
- spin_unlock(&kobj->kset->list_lock);
- }
create_dir函数定义如下:
- staticintkobject_add_internal(structkobject *kobj)
- {
- interror = 0;
- structkobject *parent;
- if(!kobj)
- return-ENOENT;
- if(!kobj->name || !kobj->name[0]) {
- WARN(1, "kobject: (%p): attempted to be registered with empty "
- "name!\n", kobj);
- return-EINVAL;
- }
- parent = kobject_get(kobj->parent);
- /* join kset if set, use it as parent if we do not already have one */
- if(kobj->kset) {
- if(!parent)
- parent = kobject_get(&kobj->kset->kobj);
- kobj_kset_join(kobj);
- kobj->parent = parent;
- }
- pr_debug("kobject: '%s' (%p): %s: parent: '%s', set: '%s'\n",
- kobject_name(kobj), kobj, __func__,
- parent ? kobject_name(parent) : "<NULL>",
- kobj->kset ? kobject_name(&kobj->kset->kobj) : "<NULL>");
- error = create_dir(kobj);
- if(error) {
- kobj_kset_leave(kobj);
- kobject_put(parent);
- kobj->parent = NULL;
- /* be noisy on error issues */
- if(error == -EEXIST)
- printk(KERN_ERR "%s failed for %s with "
- "-EEXIST, don't try to register things with "
- "the same name in the same directory.\n",
- __func__, kobject_name(kobj));
- else
- printk(KERN_ERR "%s failed for %s (%d)\n",
- __func__, kobject_name(kobj), error);
- dump_stack();
- } else
- kobj->state_in_sysfs = 1;
- returnerror;
- }
首先确保kobj->name已经被赋值,即kobject必须有名字。如果指定了kobj->kset,则调用kobj_kset_join将kobj加入到kobj->kset中。同时,如果kobj->parent仍为NULL,则将kobj->parent设置为kobj->kset->kobj。
- staticintkobject_add_varg(structkobject *kobj,structkobject *parent,
- constchar*fmt,va_listvargs)
- {
- intretval;
- retval = kobject_set_name_vargs(kobj, fmt, vargs);
- if(retval) {
- printk(KERN_ERR "kobject: can not set name properly!\n");
- returnretval;
- }
- kobj->parent = parent;
- returnkobject_add_internal(kobj);
- }
首先调用kobject_set_name_vargs设置kob->name。然后初始化kobj->parent为parent参数指定的kobject。最后,调用kobject_add_internal将kobject注册到系统中,该函数定义如下:
- staticvoidkobject_init_internal(structkobject *kobj)
- {
- if(!kobj)
- return;
- kref_init(&kobj->kref);
- INIT_LIST_HEAD(&kobj->entry);
- kobj->state_in_sysfs = 0;
- kobj->state_add_uevent_sent = 0;
- kobj->state_remove_uevent_sent = 0;
- kobj->state_initialized = 1;
- }
首先初始化kobj->kref,实际上kobj->kref就是一个原子变量(atomic_t)。接着初始化链表项kobj->entry,并设置其他kobject成员。
- /**
- * kobject_init - initialize a kobject structure
- * @kobj: pointer to the kobject to initialize
- * @ktype: pointer to the ktype for this kobject.
- *
- * This function will properly initialize a kobject such that it can then
- * be passed to the kobject_add() call.
- *
- * After this function is called, the kobject MUST be cleaned up by a call
- * to kobject_put(), not by a call to kfree directly to ensure that all of
- * the memory is cleaned up properly.
- */
- voidkobject_init(structkobject *kobj,structkobj_type *ktype)
- {
- char*err_str;
- if(!kobj) {
- err_str = "invalid kobject pointer!";
- gotoerror;
- }
- if(!ktype) {
- err_str = "must have a ktype to be initialized properly!\n";
- gotoerror;
- }
- if(kobj->state_initialized) {
- /* do not error out as sometimes we can recover */
- printk(KERN_ERR "kobject (%p): tried to init an initialized "
- "object, something is seriously wrong.\n", kobj);
- dump_stack();
- }
- kobject_init_internal(kobj);
- kobj->ktype = ktype;
- return;
- error:
- printk(KERN_ERR "kobject (%p): %s\n", kobj, err_str);
- dump_stack();
- }
该函数首先确保kobj和ktype都存在,否则直接退出。如果该kobj进行过初始化,则打印警告信息。然后调用kobject_init_internal真正开始初始化kobj,最后把kobj->ktype设置为ktype。
- /**
- * kobject_init_and_add - initialize a kobject structure and add it to the kobject hierarchy
- * @kobj: pointer to the kobject to initialize
- * @ktype: pointer to the ktype for this kobject.
- * @parent: pointer to the parent of this kobject.
- * @fmt: the name of the kobject.
- *
- * This function combines the call to kobject_init() and
- * kobject_add(). The same type of error handling after a call to
- * kobject_add() and kobject lifetime rules are the same here.
- */
- intkobject_init_and_add(structkobject *kobj,structkobj_type *ktype,
- structkobject *parent,constchar*fmt, ...)
- {
- va_listargs;
- intretval;
- kobject_init(kobj, ktype);
- va_start(args, fmt);
- retval = kobject_add_varg(kobj, parent, fmt, args);
- va_end(args);
- returnretval;
- }
这个函数分为两部分,首先调用kobject_init函数对kobject对象进行基本的初始化。然后,调用kobject_add_varg函数将kobject注册到系统中。va_start和va_end是处理可变参数的固定语法。
- structkobject {
- constchar*name;
- structlist_head entry;
- structkobject *parent;
- structkset *kset;
- structkobj_type *ktype;
- structsysfs_dirent *sd;
- structkref kref;
- unsigned intstate_initialized:1;
- unsigned intstate_in_sysfs:1;
- unsigned intstate_add_uevent_sent:1;
- unsigned intstate_remove_uevent_sent:1;
- unsigned intuevent_suppress:1;
- };
- /**
- * struct kset - a set of kobjects of a specific type, belonging to a specific subsystem.
- *
- * A kset defines a group of kobjects. They can be individually
- * different "types" but overall these kobjects all want to be grouped
- * together and operated on in the same manner. ksets are used to
- * define the attribute callbacks and other common events that happen to
- * a kobject.
- *
- * @list: the list of all kobjects for this kset
- * @list_lock: a lock for iterating over the kobjects
- * @kobj: the embedded kobject for this kset (recursion, isn't it fun...)
- * @uevent_ops: the set of uevent operations for this kset. These are
- * called whenever a kobject has something happen to it so that the kset
- * can add new environment variables, or filter out the uevents if so
- * desired.
- */
- structkset {
- structlist_head list;
- spinlock_t list_lock;
- structkobject kobj;
- conststructkset_uevent_ops *uevent_ops;
- };
- structkset_uevent_ops {
- int(*constfilter)(structkset *kset,structkobject *kobj);
- constchar*(*constname)(structkset *kset,structkobject *kobj);
- int(*constuevent)(structkset *kset,structkobject *kobj,
- structkobj_uevent_env *env);
- };
- structkobj_type {
- void(*release)(structkobject *kobj);
- conststructsysfs_ops *sysfs_ops;
- structattribute **default_attrs;
- conststructkobj_ns_type_operations *(*child_ns_type)(structkobject *kobj);
- constvoid*(*namespace)(structkobject *kobj);
- };
- structsysfs_ops {
- ssize_t (*show)(structkobject *,structattribute *,char*);
- ssize_t (*store)(structkobject *,structattribute *,constchar*,size_t);
- };
- structattribute {
- constchar*name;
- mode_t mode;
- #ifdef CONFIG_DEBUG_LOCK_ALLOC
- structlock_class_key *key;
- structlock_class_key skey;
- #endif
- };
- /*
- * Callbacks so sysfs can determine namespaces
- * @current_ns: return calling task's namespace
- * @netlink_ns: return namespace to which a sock belongs (right?)
- * @initial_ns: return the initial namespace (i.e. init_net_ns)
- */
- structkobj_ns_type_operations {
- enumkobj_ns_type type;
- constvoid*(*current_ns)(void);
- constvoid*(*netlink_ns)(structsock *sk);
- constvoid*(*initial_ns)(void);
- };
- structkref {
- atomic_t refcount;
- };
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